That's because most people on HN are from the U.S. where a century of propaganda has convinced most people not only that poor people are lazy, but by extension that unions are evil, corrupt and lazy organizations infiltrated by organized crime. While this propaganda has a minority basis in reality in some cases, as all propaganda will have because propaganda can't be 100% fantasy and make-believe, it's an ignorant basis to take when discussing broad and general questions like unions as a concept.
If you ask someone from Spain or Germany about unions and attempt to explain why they're "evil" from the US perspective, I can guarantee you will be met with complete disbelief. Most people in Europe may not actively be a part of a union, but they normally recognize them as beneficial entities in the labor market, and as something that will help balance the scales against employers of normally vastly larger influence, both politically and economically.